1. Field of the Invention
The present invention relates to a display panel, a method of manufacturing the same, and a liquid crystal display panel having the display panel.
2. Description of the Background Art
Conventionally, as a display mode of a liquid crystal display device, a twisted nematic (TN) mode that generates an electric field in a direction vertical to a liquid crystal display panel has been widely used. Meanwhile, there is proposed a horizontal electric field mode in which liquid crystal molecules are driven in a horizontal direction by an electric field generated in a direction parallel to the liquid crystal display panel (horizontal direction). This horizontal electric field mode has an advantage in enhancing a viewing angle, and implementing high definition and high luminance, so that it is thought that this mode will become the mainstream in a small/medium size panel such as a smartphone or a tablet especially.
The horizontal electric field mode includes an in-plane switching (IPS) mode and a fringe field switching (FFS) mode. A FFS mode liquid crystal display device includes a lower electrode, an upper electrode having slits, and an insulating film provided between those electrodes, and one of the lower electrode and the upper electrode is used as a pixel electrode, and the other is used as an opposed electrode. When a voltage is applied between the pixel electrode and the opposed electrode, an electric field is generated in the liquid crystal layer in roughly a horizontal direction, and the liquid crystal molecules in the liquid crystal layer are driven by the electric field in the horizontal direction.
A signal line and a thin film transistor are formed below the upper electrode and the lower electrode with a protective insulating film interposed between them, in a display region of the liquid crystal display panel. The above-described electric field is generated when a certain signal (voltage) is externally applied to the lower electrode or the upper electrode through a contact hole of the protective insulating film after passing through the signal line, and the thin film transistor.
However, during an operation, parasitic capacity which causes a display quality to degrade is generated between the lower electrode and the signal line. Thus, an insulating film is formed between the lower electrode and the signal line, in order to reduce the parasitic capacity. As the insulating film, Japanese Patent Application Laid-Open No. 2007-226175 proposes using an acrylic resin film having a relatively large thickness that can reduce the parasitic capacity, and can eliminate an uneven surface of the thin film transistor.
The liquid crystal display panel includes not only the above-described display region but also a frame region surrounding the display region. The frame region includes a plurality of terminal electrodes, and a plurality of external wirings extended from the display region and connected to the plurality of the terminal electrodes, and each of the external wirings is covered with a protective insulating film that protects the external wiring from being damaged or corroded with water.
Here, in a process of manufacturing the liquid crystal display device, the terminal electrode of the liquid crystal display panel is electrically connected to an external element (such as a printed substrate or IC chip). More specifically, the terminal electrode exposed in the protective insulating film is bonded to the external element by pressure bonding through an anisotropic conductive film (ACF), whereby the terminal electrode and the external element are connected through conductive particles in the ACF.
However, in the case where the above-described acrylic resin film is formed above the external wiring in the frame region, there is a difference in height (uneven surface) roughly corresponding to a film thickness of the acrylic resin film, between the acrylic resin film formed above the external wiring, and the terminal electrode above which the acrylic resin film is not formed. Therefore, although the terminal electrode and the external element should be connected through the conductive particles in the ACF originally, they cannot be connected because the acrylic resin film is formed in the vicinity of the terminal electrode (the pressure force is dispersed to the acrylic resin film), that is, a contact defect is caused in some cases. Especially, when the external wiring and the terminal electrode are closely provided in order to miniaturize the frame region, it is thought that such problem becomes more conspicuous.
Meanwhile, in a case where the acrylic resin film is not formed above the external wiring, there is a problem that the protective insulating film to cover the external wiring and thus the external wiring are damaged in a process of manufacturing the liquid crystal display panel.